Field of the Invention:
The invention relates to the determination of a fixed noise structure which overlays the images captured using an image converter.
Digital image converters are used for the automated conversion of an optical image into digital image data which represents the optical image. Corresponding image converters are frequently also referred to as image sensors. Since the conversion properties of conventional image sensors are as a rule not ideal, the images represented in the digital image data generally exhibit differences from the optical images on which they are based. These differences are referred to as image errors.
Differences in the properties of the sensors for individual image points are for the most part the cause of the so-called “fixed pattern noise”, a fixed noise structure which, regardless of subject, overlays all the image data generated by the respective image sensor and as a result may have a detrimental effect on possibly following image processing methods. An improvement in the image quality can therefore be achieved by subtracting the fixed pattern noise from the digital image data, similar to a foreign or reference image.
To this end, the fixed pattern noise of the particular image converter must however be known. At the present time, in order to ascertain the fixed pattern noise of an image converter, the latter is used to record a dark image whose image data contains the fixed pattern noise and an offset which is constant for all image element sensors of the image converter. The offset corresponds to the average value of all the image element values. Finally, the correction values for the digital image data can be ascertained from the image data for the dark image, preferably captured at a high amplification setting for the image converter. At the present time, the ascertainment of the fixed pattern noise is carried out towards the end of the image converter manufacturing process as an additional production step. On the one hand, a lightproof covering of the photosensitive surface of the image converter is required in this situation, and on the other hand the correction values based on the fixed pattern noise must be accessibly stored in a data memory associated with the image converter if an image data correction is to be possible during operation of the image sensors. The separate determination of the fixed pattern noise prior to a commissioning of the image converter signifies additional costs associated with an increased logistical resource requirement.